Resource Directed Measures for Protection of Water Resources: River Ecosystems
SECTION E:
PROCEDURE FOR INTERMEDIATE DETERMINATION OF RDM FOR RIVER
ECOSYSTEMS
Senior Authors (in alphabetical order):
Andrew Bath, Ninham Shand Consulting Engineers
Sebastian Jooste, Institute for Water Quality Studies, Department of Water Affairs and Forestry
Delana Louw, IWR Environmental
Heather MacKay, Institute for Water Quality Studies, Department of Water Affairs and Forestry
Nico Rossouw, Ninham Shand Consulting Engineers
Contributing Authors:
Peter Ashton, Environmentek CSIR
Brendan Hohls, Institute for Water Quality Studies, Department of Water Affairs and Forestry
Carolyn Palmer, Institute for Water Research
Editors:
H MacKay, Department of Water Affairs and Forestry
L Guest, Guest Environmental Management
Version:
1.0
Date:
24 September 1999
D:\..\f_rdm_october\rivers\version 1.0\riv_sectionE_version10.doc
Ed’s notes:
1. Change outdated IFR terminology
2. Review text layout for improved accessibility and readability
3. Clarify integration of water quantity & water quality
4. Check cross references to appendices
5. Check literature references
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Resource Directed Measures for Protection of Water Resources: River Ecosystems
Section E: Procedure for Intermediate Determination of RDM
for River Ecosystems
E.1
What is in this section
This section covers the procedures for intermediate determination of resource directed measures for river
ecosystems.
The intermediate procedure differs substantially from desktop and rapid procedures in that specialist field
surveys for hydraulics, water quality, habitat and biota are an integral part of the procedure and must be carried
out in certain specific places in the overall procedure.
At the intermediate level:
 the method is based on actual hydraulic calibrations at selected sites, and not solely on quaternary
catchment hydrology;
 there is explicit integration between the water quantity and water quality components of the Reserve;
 relevant resource quality objectives for instream and riparian habitat and for instream biota can be
determined qualitatively or semi-quantitatively, depending on how much historical data is available;
 relevant resource quality objectives for water uses and land-based activities can be determined qualitatively.
The intermediate procedure follows the seven generic steps for RDM determination. The overview of the
procedure is given in this Section E, with cross-references in the text to relevant appendices providing specialist
procedures for:
 selection of survey sites;
 hydraulic calibrations;
 habitat integrity assessment;
 biotic integrity assessment (fish and invertebrates);
 assessments of ecological importance and sensitivity, social importance and economic importance;
 hydrological analysis and calculations for the water quantity component of the Reserve;
 analysis of past IFR studies for use in extrapolation to other rivers.
E.2
Overview of tasks in intermediate determination of RDM
The intermediate determination of RDM follows the generic RDM procedure shown in section A, Figure A1.
However, for river ecosystems, the steps in the generic procedure can be broken down into a number of distinct
tasks, some of which are conducted in parallel, and some of which are sequential. Figure E1 shows a task
breakdown of the work to be conducted in an intermediate RDM determination. The tasks have been numbered
with Roman numerals (I to XIX) to avoid confusion with the steps in the generic procedure.
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Resource Directed Measures for Protection of Water Resources: River Ecosystems
I. Delineate boundaries of
study area
II. Delineate boundaries
of resource units
III. Determine
ecoregional type
IV. Select survey sites
V. Cross sectional survey
Hydraulic calibration
Photopoint monitoring
VII.
Hydrological
analysis
VIII.
Hydraulic data collection
Photopoint monitoring
VI. Inform team of site
locations and characteristics
X. Biological
information
collection &
processing
XI. Geomorph.
information
collection &
processing
XII. Water quality
information
collection &
processing
IX. Hydraulic
modelling
XIII. Reference conditions; present
status assessment; importance rating
XIV. Identify achievable
management classes OR management
class set through default rule
XV.
Determine design IFRs
Determine modelled IFRs
XVI.
Determine water quality
component
XVII.
Determine relevant RQOs
XVIII.
Matching between resource units
Integration between quantity and quality
XIX. Reporting:
Draft notice of RDM
Supporting technical reports
Monitoring programme design
Figure E1: Task flow for intermediate RDM determination
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Task I. Delineate boundaries of study area
In general, the geographic boundaries of the resource are defined by the terms of reference of the study. If the
Department initiates the study as part of a compulsory licensing process, then the boundaries are catchment
based and determined by the relevant water management agency. If Reserve is determined for the purpose of
evaluating a single water use licensing application, then the study boundaries will depend on the scale and
extent of the impact of the proposed water use.
a)
Delineate boundaries for the water quantity component:
The boundaries for the water quantity component will most often be defined by the terms of reference of the
study. However, the specialist team should also advise on modification of these boundaries or expansion of the
boundaries in order to take account of critical upstream-downstream dependencies.
An RDM determination may be required for a certain reach of river, but not for the whole river from source to
mouth. In such a case, the downstream boundary of the RDM determination may be estimated by checking for
the next major confluence downstream of the river reach of interest, at which the flow contribution of that reach
of interest can no longer be resolved from the “noise” in the hydrological record.
b)
Delineate boundaries for the water quality component:





Select a complete river catchment system, or section of a river system (as in the case of an individual
license application)
Compile a map of the study area. This can either be a GIS map generated from available information
or it can be compiled from available maps. To compile a study area map from available maps, obtain
all 1:50 000 maps for the catchment. Combine the 1:50 000 maps into a single catchment base map.
Obtain all reports and information relevant to water quality in the study area from the Department of
Water Affairs & Forestry and other potential information sources.
On the base map, mark the catchment boundary, ecoregion (level 1) boundaries, major tributaries,
major land use activities, reservoirs and routine water quality monitoring points.
For each monitoring point, indicate on the map the number of water quality samples and length of
record (for example 1974 to 1998, n=345 samples)
Obtain from the DWAF Regional office or the Catchment Management Agency, the location of
pollution monitoring stations in the study area and other non-point sources that impact on water quality.
Mark this information onto the base map.
Tasks II and III.
a)
Delineate resource units within study area
Delineate resource units for the water quantity component:
Delineate ecoregional boundaries to level II (see Appendix R1), and undertake desktop stream classification. at
desktop level (see Appendix R2).
b)
Delineate resource units for the water quality component:
Sub-divide the study area into water quality reaches which would each have an independent statement of the
water quality component of the Reserve. The objective is to sub-divide the river into water quality reaches
which, in unimpacted conditions, would have homogeneous background water quality characteristics. The size
of the reaches for the water quality component would probably differ from the water quantity resource units
because the water quantity and habitat components are usually closely aligned with level II ecoregional types
whereas water quality in rivers is more closely related to geological regions and probably more closely aligned
with level 1 ecoregional types. In many cases, the minimum size of a resource unit for water quality purposes
would be more or less equivalent to a quaternary catchment. Below are some guidelines for sub-dividing the
river into water quality reaches.
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



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
c)
After mapping the study area (Step I), identify the reservoirs in the system. The dam wall forms the
upstream boundary of a water quality reach and the inflow point into the reservoir forms the downstream
boundary of a water quality reach.
Identify the level I ecoregion boundaries. These then become the downstream boundary of a reach, and the
upstream boundary of next downstream water quality reach.
Identify the water quality monitoring point closest to the downstream boundary of each river reach. This
monitoring point will become the site where the present ecological state will be defined.
If there is no monitoring point close to the downstream boundary, the next downstream monitoring point
can be used to determine the present state provided this monitoring points falls within the upper quarter of
the next downstream reach.
If there is no monitoring point in a water quality reach, the water quality component of the reserve should
be assigned without any reference to the present state of the water quality river reach.
The breakdown of the water quality reach can be further resolved according to management requirements.
For example, where there are markedly different land uses, that have major impacts on water quality along
a water quality reach, a further breakdown according to major land uses can be done.
Delineate resource units for resource quality objectives:
Generally the resource unit boundaries for resource quality objectives (habitat and biota) will match the
ecoregion level II boundaries (see Appendix R1). In certain cases, for example particularly sensitive or diverse
habitats, the resource units boundaries may be matched to the stream classification boundaries (see Appendix
R2).
Task IV.
a)
Select survey sites within study area
Select survey sites for the water quantity component:
The water quantity component is assessed at various sites in the river called IFR sites. A cross-sectional survey
is undertaken at each IFR site to determine the profile of the river channel and, according to habitat
requirements, the various hydraulic parameters such as depth, wetted perimeter and velocity. These parameters
are converted to flow by the hydraulic modelling to determine the flow component of the Reserve, hereafter
referred to as IFRs. Normally, four IFR sites are selected to represent a river reach of about 200 km in length.
The fewer IFR sites, the less accurate the IFR results will be, as only a limited number of IFR sites are assumed
to represent all the variety of habitats that could occur along the length of the river.
The comprehensive RDM determination method will be applied for large and/or important rivers. The IERM
(Quantity) will probably be more relevant for smaller rivers and smaller developments. The impacts on flow of
smaller developments would be apparent for a shorter stretch of river than where large developments are being
planned. It is therefore assumed that two IFR sites will be selected for a river reach of between 70 and 100 km
in length. This decision will be based on the results of step 1, 2 and 4 and is therefore an ad hoc decision that
will depend on the specific impact of the development amongst others. The quantification of the requirements
for water quantity component of the intermediate ecological Reserve will be based on two survey sites.
The IFRs are determined at IFR sites which have to provide a variety of habitats, providing the clues required
for the specialists to determine the IFRs.
The detailed method for selecting IFR sites is described in Appendix R22. Ideally, the selection requires the
habitat integrity video and the input of a multi-disciplinary team. For the purpose of the IERM (Quantity), it is
recommended that the same principles are utilised wherever possible when selecting the IFR sites, but it is
acknowledged that a video is unlikely to be available in most cases, and sites will be selected based mostly on
the accessibility of sites, within the time constraints. Due to the lack of time available prior to the specialist
meeting only one hydraulic calibration, over and above the observations made during the site selection visit, will
be possible. However, the value of the second calibration will depend on how different the two calibrations are
as within a period of two months, very similar flows could be experienced. The site therefore has to be as
hydraulically simple as possible to facilitate modelling of the hydraulic relationships from possibly a single site
observation, but should still provide as many ecological clues as possible, i.e. provide a variety of habitats at
different flows.
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As the IERM (Quantity) is a 'scaled-down' version of the BBM, the same effort cannot be applied when
selecting sites. The site selection will therefore be undertaken by two specialists:
 Hydraulician
 An aquatic scientist with a basic understanding of the habitat requirements of the various biotic components
and of the river's functioning. This person will require experience of BBM site selection and specialist
meetings to understand the criteria most often used in selecting sites by the fish, aquatic invertebrate,
riparian vegetation and fluvial geomorphology specialists. It would be an advantage if this person was one
of the specialists. However, it must be noted that only specialists that have been exposed often to IFR site
selection understand how the other specialists evaluate sites. Fish and invertebrate habitat might be seen as
the more vital habitat as these habitats are mostly used to set the base flows. All previous IFR results have
indicated that the base flow component forms the largest part of the total IFR flow volume and higher
flows/floods the smaller component; it is therefore more important to have the base flows as accurate as
possible.
This will require a two/three day site visit.
b)
Select survey sites for the water quality component:
Water quality survey sites should be selected on the basis of the breakdown of the study area into water quality
reaches, as described above. Ideally, for assessment of reference conditions and present status, there should be
one water quality survey site per water quality reach, but this might not always be possible within the coverage
of the national water quality monitoring networks.
Task V. Cross-sectional survey and hydraulic calibration
Once the IFR sites have been selected, various activities are required, such as a cross-sectional survey, hydraulic
calibration and fixed photo point monitoring. These activities provide the specialists with the river profile and
the stage discharge rating curve to determine the IFRs, as well as photographs to describe the profile at a
specific discharge.
The purpose of these activities is to
 provide a stage discharge rating curve as accurately as possible to enable specialists to relate habitat
requirements to flow rate, and thereby to determine the IFRs;
 provide photographs illustrating the habitat conditions at different flow conditions.
Methods for all these procedures are standard, and detail is provided in Appendix R17. However, it is the timing
and the use of as few specialists as possible to provide the information in a time frame suitable for the
Intermediate Ecological reserve that are specific to this method.
The following is therefore recommended:
Once the sites have been selected (Action 1) and during the same visit, the cross-sectional profiles have to be
surveyed by the hydraulic engineer and the aquatic scientist (two persons are the minimum required for the
cross-sectional profiles). The flows have to be measured if the site is not near a gauging weir (two persons are
required for a flow measurement). A temporary benchmark needs to be established. Photographs need to be
taken of this site as well as any other sites which indicate more complex ecological habitat variability and for
which the flow measurement is still valid.
Important note:
Ideally one of the hydraulic calibrations must be undertaken during the dry season or when the river is
reasonably low. If the hydraulic calibrations are undertaken when the river is in flood or indicating very high
base flows, the consequences will be the following:
 The cross-sectional surveys cannot be undertaken over an area such as a rapid with fast flowing water as it
is impossible for the surveyors to stand safely in the flow.
 The hydraulic modelling for low flows, especially drought flows, will be very, if not completely, inaccurate.
 The physical character of the habitats is not visible at high flows.
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A hydraulic engineer who understands and has experience in low flow hydraulics and IFR studies is required.
It MUST be emphasised that the calibrations will be limited, and an experienced person will therefore be
required to establish a reasonably accurate rating curve within all the limitations. The hydraulics engineer must
also be able to provide the survey and flow measurement equipment and do the work that normally would be
undertaken by a group of technicians.
The hydraulic engineer requires an assistant to undertake the cross-sectional survey and flow measurements. As
a reasonably skilled person is required to undertake this work, it is recommended that the aquatic scientist who
accompanies the hydraulics engineer to select the sites also act as a 'hydraulic' assistant.
Task VI.
Inform team of site locations and characteristics
The co-ordinator must e-mail all the specialist members of the team, providing information on:
 the co-ordinates of each site;
 a short description of the habitats present;
 photographs of the sites.
This can be done immediately after the cross-sectional and hydraulic surveys.
Task VII.
Hydrological analysis
A standard hydrological provision of data is provided as part of the IERM based on the hydrological information
available (see Appendices R16 & R13). During the IFR specialist meeting, all IFRs specified during the IERM
study are checked against the hydrology for accuracy and realism, and adjusted if proved inaccurate or
hydrologically unrealistic. The hydrological information required is daily virgin hydrology for each site and the
accuracy is dependent on gauging weirs in the vicinity with reasonable records. This will probably not be the
case for most of the rivers for which the IERM (Quantity) will be applied and the DSS as for the Desktop and
Rapid methods (see Appendix R13) will then be used.
The purpose of this task is to be able to determine the realism of the IFRs against realistic hydrology and, where
the ecological clues or the hydraulics are inadequate, to guide the determination of IFRs.
This method will be two-fold depending on the type of data available. The two approaches are as follows:
 If there are gauges located in the system with sufficient length of suitable data available, the standard BBM
IFR hydrological approach can be followed using the HYMASS software. This could require additional
time what will be recommended and will result in a higher confidence IFR result. The approach is
described in detail in Appendix R16.
 If no hydrological data (except for WR 90) is available, the Hughes DSS will be used. This approach is
described in detail in Appendix R13.
Expertise required: a hydrologist who can apply the above methods.
Time required for this task will depend on the type of information available. For the sake of costing the
procedure, a standard of 2 days will be used.
Task VIII.
Hydraulic data collection and photopoint monitoring
The purpose of this task is to provide
 Additional stage-discharge and hydraulic information with which to calibrate the hydraulic model and
thereby providing more accurate answers;
 additional photographs to illustrate habitats under different flow conditions than those during the site
selection visit.
A site visit must be undertaken at different flows (if possible) than the flow data collected during the first site
selection visit.
Expertise required: hydraulician accomplished in low flow and IFR hydraulics and an assistant. The person
responsible for the photopoint monitoring should act as the assistant.
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Time required: one day for two sites, with half a day travel where necessary.
Task IX.
Hydraulic modelling
The purpose of this task is to provide a stage discharge rating curve, i.e. a stage vs. discharge relationship.
Applicable hydraulic modelling should be applied. This is described in detail in Appendix R17.
Expertise required: hydraulic engineer accomplished in low flow and IFR hydraulics.
Time required: one day per site, i.e. two days and a half a day for plotting the survey data and half a day for
surveying and illustrating trees on the profiles, i.e. 3 days in total.
Task X.
Collection and processing of biological data
During a comprehensive determination, the specialists have the opportunity to collect biological information at
least twice at the IFR sites, once during the site selection visit and on one other occasion. The surveys
undertaken during those visits as well as any information obtained previously/historically will provide the
specialists with the knowledge of the species that occur in the area, aid them to identify sensitive / indicator
species and the habitat requirements of these species. This information will be utilised to assess the IFRs.
As the IERM (Quantity) is a "scaled-down" version of the BBM, a desktop study only should form part of the
work prior to the specialist meeting.
The purpose of this task is to provide the specialists with information within their disciplines to enable them to
determine the IFRs.
Whereas the BBM is based on knowing which species occur in the river and defining their habitat requirements,
a different approach will have to be followed for the IERM (Quantity). As insufficient time will be available to
the specialists prior to the specialist meeting to undertake field surveys, the following approach will be required:
 Obtain information of any prior surveys in the river.
 Determine, based on the above as well as specialist knowledge of the biota occurring in the area or region,
the type of species that could possibly occur in the river and the habitat that would be required to cater for
those species.
 Write a short, two page document summarising this information.
NOTE : If no biological information is available at all for the river in question, the time available to collate
available information would be better spent on a field survey.
Expertise required: due to the limited opportunities for undertaking surveys, it is vital that local specialists, if
available, form part of the multi-disciplinary team. The IERM, as for the BBM, is based on expert judgement
and best available information. It is therefore imperative that the aquatic scientists with personal knowledge on
the river be involved. However, as the IERM is more reliant on expert judgement than the BBM, it is more
important that the involved specialists have sufficient experience to be able to determine the IFRs with
extremely limited knowledge of the system.
Input from the following experts is required:
 Fish specialist;
 Aquatic invertebrate specialist;
 Riparian vegetation specialist. No data base exists for riparian vegetation and it would therefore seldom be
required for the riparian vegetation specialist to undertake preparatory work.
Time required: one day for each specialist.
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Task XI.
Collection and processing of geomorphology data
A geomorphological description of the river and an understanding of the extent and direction of channel change
is important in the Intermediate Reserve Process. Many flow requirements are based on this information
therefore IFRs have to take cognisance of this trajectory of channel morphology change.
The purpose of this task is to provide evidence for historical change in the river channel.
Interpretation of aerial photographs provides a relatively quick and accurate method of determining channel
morphology change. A range of aerial photographs is used to include IFR sites and other sensitive areas. A
wide range of time intervals are required at a suitable scale (1: 20 000). These photos can be hand traced to
clearly illustrate physical changes in the river channel.
Expertise required: fluvial geomorphologist with sufficient IFR experience.
Time required: one day.
Task XII.
Collection and processing of water quality data
The intermediate determination of the water quality component of RDM relies primarily on available historical
water quality data, supplemented by short term monitoring if required.
Select a water quality data point in each water quality reach that has the following attributes:
 A data record that extends over a period of at least two years and contains at least 60 data records.
 The monitoring point should be representative of the “minimum impact” condition within the ecoregion,
thus the point should be upstream of point sources and areas of diffuse drainage, or outside mixing zone
boundaries.
If there is no monitoring point that meets this criteria or there are large distances between monitoring points
where water quality appears to be modified substantially from upstream sites, a short term monitoring program
is required.
 Implement a weekly monitoring for a period of 60 days to gather the necessary information to undertake an
intermediate RDM (water quality) determination.
Task XIII(a). Determine reference conditions
i)
Determining reference conditions for the water quantity component:
Reference conditions for the water quantity component are represented by the virgin hydrology, which is
prepared as part of Task VII.
ii)
Determining reference conditions for the water quality component:
Background
This section covers the method to describe a water quality reference condition for a particular water quality
river reach. It should be noted that the method has been developed for rivers and thus has not been tested
using data sets for impoundments, wetlands or estuaries. Water quality constituents include: system
variables (total dissolved solids (TDS), pH, dissolved oxygen (DO), suspended solids, and water
temperature), nutrients (these include ammonia, soluble phosphorus and the N:P ratio), and toxic
substances (organic and inorganics).
The determination of the reference condition forms an integral component of the reserve determination.
The water quality reference condition is used to describe the natural unimpacted characteristics of a
particular water quality resource unit (i.e. in a particular resource unit prior to the influence of humans).
The reference conditions are used in: (1) assessing the present ecological status of the ecoregion to assess
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the degree of modification from the unimpacted state, and (2) in the quantification of the Ecological
Reserve.
Reference conditions present a baseline for assessing the water quality in a particular water quality river
reach. Ideally, the reference condition should be stable and not vary over time. It is however accepted that
there will be a seasonal variation in the reference condition caused by differences in the drainage processes
during the summer and winter periods. It should also be noted that the reference condition for a particular
system variable (such as TDS, DO, temperature, pH & SS) can change along the length of most rivers.
This variation is a result of changes in the natural basin characteristics associated with the geology, soils,
elevation, climate, topography, vegetation and runoff properties of the basin.
Longitudinal variation in quality can be brought about by changes in the natural drainage characteristics
(as described above) as well as by anthropogenic factors such as the discharge of effluents from point
sources. In the definition of point sources, it is assumed the effluent is delivered to the river from a pipe,
canal or other structure. Where effluent is derived from a wastewater treatment works, information is
usually available on the flow and quality of the effluent so that it is possible to estimate the load input to
the river.
Diffuse drainage from urban and agricultural areas (another anthropogenic impact) also causes changes in
the quality of rivers. As is the case with irrigation return flow (water returning to the river from irrigated
land), the drainage is delivered through numerous inlets to the main channel. Unlike point sources, diffuse
sources are difficult to quantify and some form of numerical analysis is usually required to estimate the
loading rate entering a river.
In an ideal situation, Reference Conditions would be determined by analysing water quality data that was
collected before anthropogenic changes were made to the catchment. In this way, it would be possible to
use present-day data to determine the degree of modification of the river system. The Department of Water
Affairs and Forestry operates the national surface water quality monitoring program (termed the
Hydrological Information System). The system involves the collection of routine water samples from some
1700 monitoring points. Data collection in a few rivers started in the 1960's. In most rivers, data collected
began in the 1980's. Thus, at best there is a maximum period of over 30 years for a few rivers. The number
of samples collected over a given period is not consistent and in some instances is weekly, while at other
points it is monthly. Unfortunately, in most rivers, the data record begins in the early 1980's when many
rivers catchments were already influenced by land and water resource development. Thus, the Reference
Conditions can not be “read” directly from the historic data set but rather a certain degree of data analysis
is required to derive the necessary information. In some rivers that are deficient in water quality data, it
will be necessary to use information from neighbouring rivers (in the same ecoregion) to define the
Reference Condition.
As diffuse sources are more challenging to quantify than point sources, it is difficult to completely
“remove” this impact from the present condition. Thus, in most rivers the Reference Condition does not
represent pristine riverine state but a description of the minimum impact baseline. The user of the method
should therefore use all available information sources (in addition to the HIS data set) to derive the
reference condition, and where there is a deficient amount of information, such water quality resource units
must be “flagged”.
The aim is to set Reference Conditions for each water quality river reach along the main stem of the river
channel. Ideally, a minimum of one water quality monitoring point should be located on the main channel
in each water quality river reach. Unfortunately, there are many rivers that have little or no water quality
data, or the data points are located downstream of effluent discharges and drainage canals.
Method
1. Select a water quality data point in each ecoregion that has the following attributes:
 A data record that extends over a period of at least two years and contains at least 60 data records.
 The monitoring point should be representative of the “minimum impact” condition within the
ecoregion, thus the point should be upstream of point sources and areas of diffuse drainage.
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If there is no monitoring point that meets this criteria or there are large distances between monitoring
points where water quality appears to be modified substantially from upstream sites, a short term
monitoring program is required. Implement weekly monitoring for a period of 60 days to gather the
necessary information.
2. For each monitoring point within a water quality river reach, the following tasks are required:
 Plot a time series of all system variables (use the software on the IWQS web site 1),
 For each system variable plot a time series, and identify if a trend exists.
It should be noted that rivers can show a positive or negative trend. A positive trend could be caused by
an increasing degree of contamination over time, and a negative trend associated with an improvement
in riverine quality associated with effective management of the system. It is also necessary to plot a
time series of river flow to show both the seasonality as well as identify periods of high and low runoff.
In the early 1980s and 1990's, extended droughts across most of the country caused an increase in the
concentration of TDS and nutrients. Special note must be made to this in assessing trends because the
lead time into the drought brought about a considerable deterioration in water quality of many rivers in
South Africa.
 Where a trend exists, the reference condition is determined from the period with the water quality
least modified from natural.
 For the selected period, determine the 25, 50 and 75 percentiles for each system variable (using the
IWQS software) and tabulate the monthly values.
 Plot the annual 25, 50 and 75 percentiles for each system variable to assess the longitudinal
gradient along the river channel for each water quality resource unit.
Should there be a marked increase in any one system variable (of greater than 100% in the median of
the upstream value), then the water quality resource unit should be divided laterally into two, and the
process repeated so that the monthly reference condition are specified for the new water quality
resource unit. It should also be noted that in some rivers, there will be minimal longitudinal gradients
so that the Reference Condition in the upper reaches could be used for downstream ecoregions.
3. Water temperature - There may not be measured data for temperature so it is necessary to determine a
theoretical water temperature. Studies have been carried out to fill in long sequences of water
temperature using measured sequences of air temperature. The general finding is that river water
temperature is usually between 1 and 2 degrees cooler than the 2 day moving average daily air
temperature (14h00 reading) Görgens et al. (1993). Thus, it is possible to make a preliminary estimate
of the river water temperature based on the local air temperature. Using the Weather Bureau data set, it
is possible to derive a monthly sequence of median monthly air temperature, that can then be used to
derive a median monthly water temperature.
4. Dissolved oxygen: There may be no measured data so it is necessary to determine the theoretical
saturated dissolved oxygen concentration. Appendix A lists two methods to derive theoretical dissolved
oxygen concentration at 100 percent saturation from water temperature and altitude above sea level.
5. Nutrients: For the nutrients, phosphorus and nitrogen, it is assumed that the reference condition is
specified by the A class limits, which are indicated by the Target Water Quality Ranges (TWQRs)
stated in the South African Water Quality Guidelines for Aquatic Ecosystems (DWAF, 1997). Until
such time as research has been carried out to assess possible regional differences in the nutrient regimes
in the different ecoregions then the reference conditions will be taken from the A class that represents
the unimpacted condition. Should sufficient data be available, then site-specific reference conditions
may be derived.
1
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Table E1: Generally applicable reference conditions for nutrients
Nutrient descriptor
Value of Reference Condition (equivalent to an
Assessment Class of A)
Ammonia (expressed as un-ionised NH3 in mg-N/)
<0.007
SP:TP ratio
<10 percent
N:P ratio where [SP] is <0.01 mg/
10:1
N:P ratio where [SP] is <0.05 mg/
20:1
6. Suspended solids: In the absence of suspended solids data (SS or turbidity) it is necessary to use
expert opinion to assess the SS for low and high flow conditions. In support of this, refer to Rooseboom
et al. (1992) sediment yield maps for RSA to delineate catchment areas which display low, medium and
high sediment exports. Thus, only a qualitative statement is made where no measured data are
available.
7. Toxic chemicals: For toxic organic and inorganic chemicals, it is assumed that the reference condition
is specified by the A class limits, as indicated by the TWQRs stated in the South African Water Quality
Guidelines for Aquatic Ecosystems (DWAF, 1997). However, site specific information on the “natural”
presence of certain metals will result in some site-specific modification of the values, as described in
the South African Water Quality Guidelines for Aquatic Ecosystems.
8. Accounting for point sources in a water resource unit: Where a point source discharges into the water
quality river reach upstream of the monitoring point it may be necessary to modify the reference
conditions to remove the influence of the point source. This can be achieved by :
 Determining the median flow and quality concentrations of the effluent,
 Using a mass balance calculation, subtract the point source load from the river to derive the
unimpacted concentration for the upstream point. As the result will be approximate, it is necessary
for only the 50 percentile to be calculated.
9. Accounting for diffuse sources: Where a water resource unit receives extensive return flow from
diffuse sources (either urban or agricultural) it is necessary to estimate the approximate unimpacted
condition of the river. This may only be achieved by (i) comparing the reference condition with the RC
for other rivers and tributaries in the same region., (ii) using information from reports and other studies,
and (iii) using numerical methods to “remove” the diffuse source influence on river quality.
10. Documentation of reference conditions: It is essential that the methods used to determine the reference
condition are documented for review on a local and regional basis. The degree of confidence should be
stated to identify, and flag, water resource units where additional information/data will be required to
determine the reference conditions.
iii) Determining reference conditions for habitat and biota:
Generally, reference conditions for habitat and biota should be inferred from the ecoregional type of the
resource unit. The relevant ecological specialists are asked to qualitatively describe reference conditions
for their component (geomorphology, invertebrates, fish etc) when carrying out the present status
assessment and during the specialist workshop.
Task XIII(b). Assessment of present status
i)
Assessment of present status for the water quantity component:
Present status for water quantity is represented by present-day hydrology (measured or simulated). This
information is provided as part of Task VII.
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ii)
Assessment of present status for the water quality component :
This section describes a method to determine the present ecological status of a river with regard to water
quality. The method has not been tested for impoundments, wetlands or estuaries. The water quality
constituents described include: system variables (total dissolved solids (TDS), pH, dissolved oxygen,
temperature and total suspended solids), nutrients (these include ammonia, phosphorus partitioning and the
N:P ratio), and toxic substances.
The aim is to describe the current water quality at the downstream boundary of the water quality reach. If
there is no routine water quality sampling point at the water quality boundary then no present state is
defined for that water quality river reach.
For an intermediate reserve determination, additional water quality data must be collected over a period of
six to eight weeks to collect data where none is available, or to collect information that is not routinely
monitored by DWAF or other agencies. The monitoring should be used to augment the national rivers
monitoring network to collect data where there is inadequate coverage by DWAF sampling stations to
assess the water quality status. Physical measurements such as temperature, dissolved oxygen and TSS are
not often monitored on a routine basis and there is opportunity to collect limited data in the study area.
Monitoring can also include toxicity tests and a scan of heavy metal concentrations at selected sites to
determine the presence of toxic substances that would have a negative impact on the aquatic ecosystem.
1. Assessing the present status for system variables: Total dissolved salts (TDS)



For the water quality river reach, extract the TDS data for the last three years of data.
Calculate the median value for each month (using the IWQS web site software) 2.
Assign a water quality assessment category for each month using Table E2.
Table E2: Present status assessment categories for total dissolved salts (TDS)
Assessment category
Median monthly TDS (mg/l)
A
0 – 163
B
163 – 228
C
228 – 325
D
325 – 520
E and F
> 520
Exclusions: This method can not be used rivers in the eastern Cape and Western cape with high baseline salinity
values. In these cases, site-specific reference conditions will need to be determined, and the assessment
categories must be adjusted accordingly.
2. Assessing the present status for system variables: pH



2
Extract the pH data for the past three years of data.
Calculate the median pH value for each month (using the IWQS web site software).
Assign a water quality assessment category for each month using table E3.
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Table E3: Present status assessment for pH in rivers.
Assessment Category:
A
B
C
D
E&F
PH
The median pH value differs from
the upstream Reference Condition
(RC) by a maximum of:
5%
7%
10 %
12 %
>12 percent
PH
Or, the median pH should differs from
the upstream Reference Condition
(RC) by a maximum of:
0.5 pH units
0.7 pH units
1.0 pH units
1.2 pH units
>1.2 pH units
3. Assessing the present status for system variables: Dissolved oxygen concentration



For the particular water quality reach, obtain all the dissolved oxygen data for the last three years
of data.
Convert the dissolved oxygen concentrations into percentage saturation taking account of the water
temperature and elevation above mean sea level (Refer to page 59, Aquatic Ecosystem Guidelines,
DWAF, 1996 or Addendum E-1).
Calculate the median dissolved oxygen saturation for each month, and assign the monthly water
quality assessment category using Table E4.
Table E4: Present status assessment for dissolved oxygen.
Assessment category
Dissolved oxygen concentration (%)
A
80 - 120 % of saturation
B
80 - 100% of saturation
C
60 - 80% of saturation
D
40 - 60% of saturation
E&F
< 40% of saturation
4. Assessing the present status for system variables: Water temperature
Water temperature data is not always available on the Department’s water quality databases. Carry out a
qualitative assessment, using available data and information, to assess whether there are significant
artificial changes to the water temperature which may be of concern in the river reach under consideration,
beyond the ranges indicated in the South African Water Quality Guidelines for Aquatic Ecosystems
(DWAF, 1997). If this is a concern, briefly document the spatial and temporal scale of the impact, the
magnitude and the significance of the changes.
5. Assessing the present state for system variables: Total suspended solids concentrations
Suspended solids data is not always available on the Department’s water quality databases. Carry out a
qualitative assessment, using available data and information, to assess whether there are significant
changes in the suspended sediment concentration (or turbidity) which may be of concern in the river reach
under consideration, beyond the ranges indicated in the South African Water Quality Guidelines for
Aquatic Ecosystems (DWAF, 1997). If this is the case, briefly document the spatial and temporal scale of
the impact, the magnitude and the significance of the changes.
6. Assessing the present status for nutrients: Ammonia

For a particular water quality reach (downstream boundary), extract all the ammonium data for the
last three years. If the number of data records is less than 60, use a longer period of data. Ideally,
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


all nutrient classification must use the same period of data (it may not be valid to use ammonium
data for the early 1980's with phosphate data for the late 1990's).
Convert the ammonium values into un-ionised ammonia using information on water temperature
and pH (refer to Addendum E1 of this section, or page 24 in the South African Water Quality
Guidelines for Aquatic Ecosystems (DWAF, 1997) for methods to convert ammonium data to unionised ammonia concentrations.
Calculate the 90 percentile ammonia value. Where the ammonia concentration is at or near, the
analytical detection limit, the river is allocated a A/B category.
Assign the water quality assessment category for ammonia using Table E5.
TableE 5: Present status assessment for nutrients using the un-ionised ammonia concentration
General categories for nutrient
assessment
Assessment Categories
Ammonia (un-ionised)
concentration (expressed as mgN/l as NH3)
Unimpacted
A
<0.007
Moderately impacted
B
<0.015
C
<0.030
D
<0.070
E
<0.100
F
>0.100
Highly impacted system
7. Assessing the present state for nutrients: The ortho-phosphate to total phosphate ratio






For a particular ecoregion, extract all the ortho-phosphate (SRP) and total phosphorus (TP) data
for the past three years. Where there is no TP data then this method can not be used.
For each pair of SRP and TP values, determine the percentage ortho-phosphate content, given by:
Ortho-phosphate content = [SP]/[TP]*100
where [SP] is the soluble orthophosphate concentration (expressed in mg-P/l), and [TP] is the total
phosphorus concentration (expressed in mg-P/l).
In a river where the measured orthophosphate concentration is at or near, the analytical detection
limit, the river is allocated an A/B assessment category.
Calculate the median ratio value, and assign the water quality assessment category for
orthophosphate using Table E6.
Table E6: Present status assessment of nutrients based on orthophosphate as a percentage of the total
phosphorus content
General category intervals for
nutrient assessment
Oligotrophic
Mesotrophic
Eutrophic
Assessment Category
Percentage orthophosphate
content
A
B
C
D
E
F
< 10 percent
< 20 percent
< 40 percent
< 60 percent
< 80 percent
> 80 percent
8. Assessing the present status for nutrients: Nitrogen to Phosphorus ratio

For a particular water quality river reach, extract the phosphate (SRP), total phosphorus (TP),
ammonium and nitrate data for the past three years. If the number of records is less than 60, use a
longer period.
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




Calculate the total inorganic nitrogen (TIN) concentration by summing the ammonium and nitrate
values for each set of values.
Calculate the N:P ratio using the TIN and TP values
For the period of data, calculate the median N:P ratio, and the median SP concentration.
Assign the assessment category using Table E7. Where the measured orthophosphate
concentration is at or near, the analytical detection limit, the river is allocated an orthophosphate
concentration of <0.01 mg-P/l.
If there is no TP data (and only SP), use the same calculations for nitrate and ammonia to derive
the TIN concentration. The N:P ratio is then derived from the TIN and SP values and the value
assessed using Table E8.
Table E7: Present status assessment of nutrients based on the N-P ratio (using TIN and TP)
Total inorganic Nitrogen to Total Phosphorus Ratio
Ortho-phosphate
concentration
(expressed in mg-P/l)
<5:1
>5:1 & <10:1
>10:1 & <20:1
>20:1
<0.01
C
B
A
A
<0.05
D
C
B
A
<0.07
E/F
D
C
B
<0.10
F
E/F
D
C
>0.10
F
F
E/F
D/E
Table E8: Present status assessment of nutrients based on N-P ratio (using only orthophosphate data)
Total inorganic Nitrogen to Soluble Phosphate Ratio
Ortho-phosphate
concentration
(expressed in mg-P/l)
<10:1
>10:1 & <20:1
>20:1 & <30:1
>30:1
<0.01
C
B
A
A
<0.05
D
C
B
A
<0.07
E/F
D
C
B
<0.10
F
E/F
D
C
>0.10
F
F
E/F
D/E
9. Toxic substances
Data on toxic substances is not always available on the Department’s water quality databases. Carry out a
qualitative assessment, using available data and information, to assess whether there are or might be
significant impacts on the aquatic environment which can be ascribed to the presence of organic or
inorganic toxic substances in the river reach under consideration. If this is the case, briefly document the
spatial and temporal scale of the impact, the magnitude and the significance of the changes.
If there is adequate data available, then the present status with respect to toxic water quality constituents
should be assessed using the method set out in Addendum E3 of this section.
If the RDM determination is being carried out for the purpose of evaluating proposed discharge of water or
water containing waste, and inadequate data is available, then water samples must be collected weekly in
the river reach under consideration for a period of 60 days, and analysed for inorganic and organic toxic
water quality constituents of concern. The present status with respect to toxic water quality constituents
should be assessed using the method set out in Addendum E3 of this section.
10. Documentation of present status assessment
Once the present status categories have been determined, the methods, data and other supporting
information must be documented so that the calculations and assumptions can be reviewed and/or verified
later if necessary (Table E9).
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Table E9: Documentation of present ecological status - example
River: River reach:
Variable: TDS
Variable: pH
Data source used
DWAF HIS: B4H005Q01
DWAF HIS: B4H005Q01
Full data period
1974 to 1998
1974 to 1998
Trends detected
yes, positive
shift in values prior to 1990
Period used in Reference condition
1974 to 1976
1993 to 1997
Point source upstream?
None
None
Adjustment made for point sources?
Not necessary
Not necessary
Diffuse source upstream of sampling
point?
None (min. Impact)
None (min. Impact)
Adjustment made for diffuse sources?
No
No
Degree of Confidence (DOC)
High
High
Other information/notes:
-
-
The degree of confidence (DOC) is assigned from the following criteria:
High - The present state assessment is supported by studies and information available in the published
scientific literature. These studies should be directly applicable to the river in question.
Medium - The values are supported by one of the following: published studies/data, unpublished data, direct
observations.
Low – The reference conditions were based on anecdotal information, or “best estimate”.
iii) Assessment of present status for habitat and biota:
The assessment of present status for each sub-component of the habitat and biota is carried out by the
relevant specialists according to the procedures described in the appendices.
 Habitat integrity: see Appendix R4
 Riparian vegetation: see Appendix R19
 Invertebrates: see Appendix R21
 Fish: see Appendix R20
 Geomorphology: see Appendix R18
Presently, there is no formal procedure to integrate these various assessments into a quantitative or semiquantitative measure of overall present status. At the specialist meeting, expert judgement is used to
categorise the river according to the 6 assessment categories A to F (see Table E10).
For the purpose of quantifying the Reserve, integration of the various sub-component assessments into one
single index is not appropriate, as too much detail is lost. The general framework described in Appendix
R29 should be followed (R29: Using ecological management classes to set integrated resource quality
objectives and Reserve).
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Table E10: General assessment categories for ecological integrity.
CATEGORY
DESCRIPTION
A
Unmodified, natural.
B
Largely natural with few modifications. A small change in natural habitats and biota may have
taken place but the ecosystem functions are essentially unchanged.
C
Moderately modified. A loss and change of natural habitat and biota have occurred but the basic
ecosystem functions are still predominantly unchanged.
D
Largely modified. A large loss of natural habitat, biota and basic ecosystem functions have
occurred.
E
The loss of natural habitat, biota and basic ecosystem functions are extensive.
F
Modifications have reached a critical level and the lotic system has been modified completely
with an almost complete loss of natural habitat and biota. In the worst instances the basic
ecosystem functions have been destroyed and the changes are irreversible.
iv)
Assessment of present status for water uses and land-based activities
This information should be available from the regional office of the Department of Water Affairs and
Forestry. If catchment studies or situation assessments have been undertaken for the river under
consideration, these documents should provide additional detailed information to support the assessment of
present status of water uses and land-based activities which may affect the water resource.
Task XIII(c). Assessment of importance
At the intermediate level, the importance of the water resource or resource unit is assessed primarily in terms of
ecological importance and sensitivity (see Appendix R7 for detailed procedure), and social importance (see
Appendix R8 for detail). Assessment of economic importance is limited to identification and qualitative
statements of potential value of ecosystem services (see Appendix R9 for more information).
Ecological importance and sensitivity can be assessed by the relevant specialists prior to or during the specialist
meeting. If assessed prior to the meeting, then the scores can be moderated once the specialists have visited the
survey sites, which will occur during the specialist meeting.
Social importance can be assessed using limited field surveys prior to the specialist meeting. A brief report
should be prepared as for assessment of the other specialist components, and presented to the specialist meeting.
The assessment of importance is used together with the assessment of present status in the process of
determining the required management class. A high social, ecological or economic importance rating justifies
motivating for a higher level of protection (and hence a higher management class) than is currently afforded the
resource, or than would be afforded the resource under the so-called “default rule” (see the section below on
“Setting the ecological management class”).
Task XIV.
Setting the ecological management class
The detailed process for setting the ecological management class, and the consultation requirements associated
with that process, are covered in the Classification System manual. A brief overview is also given in Section A
of this document.
Where there is insufficient time for adequate consultation and field investigations (as will usually be the case in
intermediate RDM determinations), then the so-called “default rule” applies. The default rule requires that,
after an intermediate present status assessment, the ecological management class is set in relation to the present
status, but at a level which represents a goal of no further degradation for resources which are slightly to largely
modified, and at least a move toward improvement for resources which are critically modified:
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Present Status Assessment Category
A
B
C
D
E or F
Task XV.
a)
Ecological management class assigned
A
B (or higher, depending on importance rating)
C (or higher, depending on importance rating)
C (or higher, depending on importance rating)
D (or higher, depending on importance rating)
Determine the water quantity component of the ecological Reserve
Determining the design IFRs
The design IFRs need to be determined by integrating all the different requirements into a modified flow
regime. This needs to be undertaken by the various specialists visiting the IFR sites, indicating the
important components on the sites and discussing the interdependency of these disciplines in maintaining
the riverine ecosystem. A modified flow regime will be supplied for normal (maintenance) years and for
drought years.
The purpose of this task is to determine and motivate for the design IFRs.
A 1.5 day specialist meeting will be held. During the first day the design IFRs will be determined. Due to
the lack of site visits in the IERM, this specialist meeting will take place on site so that specialists have at
all times the opportunity to refer to the site itself. As this is the first opportunity for most of the specialists
to experience the site, some of the information required for other steps such as the Present Ecological
Assessment (PES) will also be addressed during this visit. The IFR site offering the most clues for a high
confidence IFR result will be visited first and these IFRs will be set in detail. The other site will be visited
afterwards during which flows extrapolated from the first site will be checked. The following will take
place during the on-site meeting:
 An aquatic invertebrate survey. The SASS process could be used as it will provide an indication of
river health and sensitive families present.
 A fish electro-shocking survey.
 An identification of riparian trees along the river.
 An investigation of the river channel and geomorphological aspects.
 A flow and water level measurement.
 The provision and motivation of a PES category for fish, aquatic invertebrates, fluvial
geomorphology, riparian vegetation.
 The determination of the Ecological Importance and Sensitivity and the Social Importance.
 A decision on the Ecological Management Class (EMC)
 Specific objectives for each component to achieve the EMC.
 A discussion and identification of base flows and floods in the key months.
 The determination of the assurance of occurrence of maintenance flows
 Motivations on a standard format will be applied by each specialist for each flow identified.
 The hydrological checking of each flow.
 The confidence in the motivations and modified flow regime specified are provided in a set format.
Motivations must be provided for the confidence supplied.
The more detailed explanation of the interactive approach followed during the determination of the IFR
(the steps listed in bold above) is set out below:
Flows are provided for both maintenance flows (those flows that will maintain the system in the
management class agreed on during years other than drought years at a certain agreed on percent of
assurance) and drought periods (flows that will only allow for survival of the most critical components of
the ecosystem). The same approach is utilised for both maintenance and drought years, starting off with
drought years.
The approach follows the following steps:
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
The maintenance and drought flows are defined by coupling an assurance based on the hydrological
typing of the river. Using the Pienaars River as an example, the format of this step is the following:
Droughts were determined as being approximately 95% exceeded based on virgin flows. Maintenance
flows were determined at approximately 50% assurance. At this stage no ecological link to determine
assurance exists, therefore the process is guided by the hydrology.
 The highest low flow (base flow) month and lowest low flow month are selected utilising the
hydrological record to make this decision. For example, in the case of the Pienaars River the months
were February and September.
 These months are used to set the low flows and the range of flows that occur during the year was
therefore fixed between the highest and lowest low flows. Note that the terminology of low flows is
similar to that of base flows.
 The low flow IFRs for the rest of the months are extrapolated from the September and February flows
following the natural shape of the annual hydrograph. This extrapolation is undertaken by the
hydrologists and checked by the ecologists.
 Each specialist provides motivations describing what the characteristics of the required flows
should be (e.g. water level, velocity, depth) and the reasons for requiring these flows. Some of the
disciplines provided primary and some secondary motivations. Primary motivations refer to
motivations provided by the disciplines that require a certain type of flow which is critical.
Secondary motivations refer to motivations provided by disciplines that could maintain the
component with less flows, but for which higher flows to satisfy the other components
requirements will not be harmful.
 After each flow is agreed on, the flows specified are checked for realism in similar years. Normal
or average hydrological years are utilised to check maintenance flows and the driest years to check
drought flows.
 During the wet season high flow events are set and motivated for. High flows refer to freshes, small,
medium and large floods. A fresh refers to a small increase in base flow. The high flows are given in
m3/s and the flow provided refers to an instantaneous peak. As the hydrology is provided in mean
daily averages, the peaks recommended are converted to slightly lower flows to reflect the mean daily
average.
 In all cases the durations of the floods are provided in days.
 The shape of the floods is based on the shape of the natural hydrograph.
 The peaks provided include the low (base) flows
 When the total volume of each flood is calculated, it excluded the low flow volume which is
already included in the total low flow volume
 A hydrological check of each flood is repeated.
An example of the format of the design IFR results is provided in Table E11.
The following are the recommended specialists to participate in the specialist meeting. As the meeting and
IFRs will be undertaken in the field, a large group cannot be accommodated.
 Hydraulics engineer
 Hydrologist
 Fish specialist
 Aquatic invertebrate specialist
 Riparian vegetation specialist
 Fluvial geomorphologist
 Facilitator
 Technical co-ordinator and integrative writer (This will usually be the team leader)
Time required: one day for each person.
b)
Modelling the IFRs
One of the basic assumptions in applying the BBM is that the specified flows, be it base flows or floods,
will not be supplied in a rigid and consistent manner, but will be linked to the natural flow regime or
natural trigger of that specific river, i.e.,
 a large flood should not be released during a month when no rains have occurred in the specific
catchment area where floods are generated;
 droughts and maintenance flows should occur during natural dry and normal periods
This assumption is also valid for the IERM.
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Table E11: Tabulated output of the specialist workshop, providing the design IFRs.
IFR SITE :
VIRGIN MAR
OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP TOTAL % of
X106 m3 MAR
IFR MAINTENANCE
LOW FLOWS
FLOW (m3/s)
DEPTH (m) section
FDC% (VIRGIN)
VOLUME (x106m3)
IFR MAINTENANCE HIGH FLOWS
FLOW (Instantaneous
peak m3/s)
DEPTH (m) section
DURATION (days)
FDC% (VIRGIN)
VOLUME (x106m3)
OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP TOTAL % of
IFR DROUGHT
LOW FLOWS
FLOW (m3/s)
DEPTH (m) section
FDC% (VIRGIN)
VOLUME (x106m3)
IFR MAINTENANCE HIGH FLOWS
FLOW (Instantaneous
peak m3/s)
DEPTH (m) section
DURATION (days)
FDC% (VIRGIN)
VOLUME (x106m3)
X106 m3 MAR
The purpose of this task is to provide the IFR results linked to a natural trigger over a historical time series., and
in a format compatible with catchment yield models currently in use.
The IFR model (see Appendix R16) provides this information. The IFR model represents an attempt to
generate a representative time series of daily flow ecological requirements that are expected to result from the
implementation of the output from an IFR workshop. The actual daily requirements are expected to be made up
of a combination of low flow releases with flood event releases superimposed upon them. In keeping with the
philosophy of the BBM and the definition of when maintenance and drought flows should occur, the model uses
climatic cues to determine the actual daily flow rates. The climatic cues within the model are derived by
examining the daily flows within a “Reference Flow” time series. This may be an observed record at an
adjacent gauging station, or a simulated time series of flows at the IFR site or elsewhere. The main
consideration in the selection of an appropriate reference flow time series is that the patterns of flow are
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representative of the patterns of flow that would have occurred at the IFR site under natural (or other suitable
development state that is considered acceptable to the specialists) conditions.
To be able to make use of the climatic cues, a set of low flow and flood “rules” are defined by the specialists.
These represent threshold values which are compared, in the model, with the daily values of the climatic cues to
determine the actual flow rate required on a specific day. The operating rules are calibrated (progressively
modified) until an acceptable pattern of time series of modified flows are achieved which satisfies the specialists
perceptions of the effects of their decision making process on the river. The graphical output of the model for
base flows for one year is illustrated in Fig. 3 and Fig 4 serves as a flow duration curve output for the model. A
statistical summary program can be provided and calculates (for each calendar month) the percentage of time
that the modified flow regime is at, or above, maintenance, between maintenance and drought or at drought
levels. These are effectively the recommended assurance levels of the different flows and are represented by a
flow duration curve (Fig. 4).
Monthly summary data or total release volumes can be generated for the complete time series. These monthly
time series data can then be further analysed to determine more detailed assurance values for the full range of
flows that form part of the recommended modified flow regime.
Expertise required: hydrologist experienced in running and calibrating the IFR model, plus other ecological
specialist team members.
Time required: half a day for each specialist.
Figure E2: Output of the IFR model as a time series
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Figure E3: Output of an IFR workshop illustrated as a FDC (Note all numbers on axis are hypothetical
and differ from river to river)
Task XVI.
a)
Determine the water quality component of the ecological Reserve
Obtaining guideline water quality classes






Obtain the future management class for the biota and vegetation components from the specialist team.
Obtain a guideline ecological management class (water quality) for the system variables, nutrients and
toxic substances using Table E12.
Note that this table only serves as a guideline, and the links between the various components (water
quantity, water quality, habitat and biota) as discussed in Appendix R29 must also be considered.
The guideline water quality management class must be made site specific by (i) testing the water
quality implications of selecting a particular guideline management class to assess the feasibility of
reaching the class given the present state, and (ii) assessing whether the changing flow conditions
could lead to non-achievement of the water quality objectives.
If the recommended flow objectives result in exceedance of the water quality objectives as a result of
natural geochemical or biophysical conditions, then the flow objectives should be adjusted until both
the flow and quality objectives can be achieved.
If the recommended flow objectives result in exceedance of the water quality objectives as a result of
point or non-point sources of pollution, then more stringent source directed measures should be
enforced rather than adjusting the flow objectives to provide “clean” water for dilution purposes.
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Table E12: Guide for intermediate determination of ecological management classes (water quality) based
on the ecological management class assigned for the biota. Note that this table applies only to intermediate
RDM determinations, and should be used in conjunction with Appendix R29.
Ecological management
class selected for the
instream/riparian biota
Guideline ecological management lass (water quality)
System variables
Nutrients
Toxic substances
A
B
B
C
C
C-D
C-D
A
B
B
C
C
C-D
C-D
A
A
A
A
A
A
A
A/A
A/B
B/B
B/C
C/C
C/D
D/D
b)
Determining the water quality component of the Reserve using the assigned management classes
(water quality)
1. Total dissolved salts
Table E13 is used to quantify the Reserve for total dissolved salts. The reserve values are based on the
class that was selected for system variables.
Table E13: System variable matrix for the assignment of the Reserve.
Ecological management class
(water quality)
Median TDS (mg/l)
A
0 – 163
B
163 – 228
C
228 – 325
D
325 – 520
Exclusions on Table E13: This method can not be used to set the water quality component of the ecological
Reserve for rivers in the Western Cape or Eastern Cape where baseline TDS is high. In these cases, the ranges
for each class must be subject to site-specific modification on the basis of water quality data from the river reach
under consideration.
2. Dissolved oxygen and pH
Table E14 is used to quantify the Reserve for pH and dissolved oxygen. The Reserve values are based on
the class that was selected for system variables.
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Table E14: Matrix for determination of the ecological Reserve (water quality) for pH and dissolved
oxygen.
Ecological
management class
(water quality)
Water quality range for a specific ecological management class (water
quality)
Median dissolved
oxygen concentration
(%)
Median pH
Median pH
The median pH value
should not differ from
the upstream reference
condition by greater
than:
The median pH value
should not differ from
the upstream reference
condition by greater
than:
A
<  5 percent
<  0.5 of a pH unit
80 - 120% saturation
B
 7 percent
 0.7 of a pH unit
80 - 100% saturation
C
 10 percent
 1.0 of a pH unit
60 - 80% saturation
D
 12 percent
 1.2 of a pH unit
40 - 60% saturation
Exclusions on Table E14: This method can not be used to set the water quality component of the ecological
Reserve for rivers in the Western Cape where baseline pH is low. In these cases, the ranges for each class must
be subject to site-specific modification on the basis of water quality data from the river reach under
consideration.
3. Water temperature and suspended sediment
The reserve for water temperature and for total suspended sediment is stated as a difference from the
baseline water quality in the study area. The allowable difference and is derived from Table E15.
Table E15: Allowable deviation from of water temperature and TSS from reference conditions for
selected ecological management classes (water quality).
Ecological
management class
(water quality)
Water Temperature
TSS
The median water
temperature should not
differ from the upstream
Reference Condition
(RC) by greater than:
Or, the median water
temperature should not
differ from the
upstream Reference
Condition (RC) by
greater than:
Where the Reference Condition
(RC) median TSS is <100 mg/l
10 percent
2o Centigrade
<10 percent
B
12 percent
3o
Centigrade
<15 percent
C
15 percent
4o Centigrade
<20 percent
20 percent
5o
<25 percent
A
D
Centigrade
(Expressed in percent change
from reference condition)
Note on Table E15: Natural seasonal variability in water temperature and TSS must be maintained.
4. Nutrients
Table E16 is used to quantify the reserve for nutrients based on the ecological management class (water
quality) selected.
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Table E16: Nutrients water quality ranges for selected ecological management classes (water quality).
Ecological
management
class (water
quality)
Water quality range for a specific ecological management class (water quality)
Median
ammonia (unionized)
concentration
(mg-N/l as NH3)
Percentage
orthophosphate
content
[PO4]/[TP]*10
0
Median
orthophosphate
concentration
(mg-P/l)
A
0 - 0.007
0 - 10 %
0 - 0.01
B
0.007 - 0.015
10 - 20 %
C
0.015 - 0.030
20 - 40%
D
0.030 - 0.070
40 - 60%
Median total
phosphorus
concentration
(mg-P/l)
TN:TP ratio
0.1
> 20:1
0.01 - 0.05
0.100 - 0.250
>10:1 & < 20:1
0.05 - 0.07
0.175 - 0.250
> 5:1 & < 10:1
0.07 - 0.10
0.167 - 0.175
< 5:1
5. Toxic water quality constituents3
In most cases, the Reserve for toxic water quality constituents is set by default at the concentrations
required for a class A river. This means that, for any toxic substances, the concentrations of that toxic
substance in the river must be :



less than or equal to the TWQR for 90% of the time;
less than or equal to the CEV for 99% of the time;
less than or equal to the AEV for 100% of the time;
The TWQR is the Target Water Quality Range stated in the SA Water Quality Guidelines for Aquatic
Ecosystems (DWAF, 1997). The acute and chronic effect concentrations to be used for a specific toxic
substance, are the AEV and CEV values specified in the South African Water Quality Guidelines for
Aquatic Ecosystems (DWAF, 1997).
If adequate data is available to assess the present status of the river reach under consideration, and if the
present status of the river reach for toxic constituents is not considered to be stressed, then the procedure
outlines in Addendum E3 of this section may be used in intermediate determination of the Reserve.
Task XVII.
Determine relevant Resource Quality Objectives
Relevant resource quality objectives should be determined at the specialist meeting. Specialists are required to
provide narrative (or quantitative where possible) requirements for habitat and biotic integrity which will
maintain the river reach under consideration in the ecological management class which is selected. Guidance on
setting of resource quality objectives for habitat and biota can be found in Appendices R23 and R29.
Resource quality objectives related to water uses and land-based activities which may impact on the water
resource under consideration may also be set if these are required. Once the full water resource classification
system has been developed, these resource quality objectives will form part of the rules associated with each
management class.
Task XVIII(a).
Match RDM between resource units
The resource directed measures set for adjacent resource units must be matched, to ensure that the RDM
specified at the downstream end of the upper resource unit will actually allow the resource directed measure in
the downstream resource unit to be achieved. In general, if a higher class is set for the downstream resource
unit, then that may place certain constraints on the selection of the classes for upstream units.
3
Editor’s note: the intermediate Reserve for toxic constituents requires additional detail.
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Task XVIII(b).
Integrate water quantity and water quality components
In the intermediate determination, the water quantity and water quality components of the Reserve should be set
in an integrated manner. There will probably not be time to set up a dynamic water quantity/quality model of
the river reach under consideration. Nevertheless, a fairly simple check such as plotting the flow-concentration
relationships may indicate where there is a need to match and integrate the water quantity and water quality
components, in order to ensure consistency (see Appendix R29).
Task XVIII(c).
Yield modelling and scenario testing
This phase does not necessarily form part of quantification of the flow component of the Intermediate
Ecological Reserve. A brief description of this is provided here, with more detail in R25. The immediate step
after calculating the Reserve is to determine the impact of the Reserve on the natural and allocable yield of the
system. This is undertaken by using the time series or assurance levels (the output from the IFR model) in a
conventional water resources assessment and reservoir yield model (such as WRYM) to determine the allocable
yield. Small, insignificant changes within the IFR which does not impact on the EMC, could have major impacts
on the yield. An interactive process between the specialists and the yield modellers are therefore required to
determine whether IFR scenarios are possible which will still achieve the EMC. Where the system has been
over-utilised so that the Reserve cannot be met, a long term strategy as part of the catchment management
strategy has to be designed. This might require various IFR scenarios to be supplied on a phased basis until the
EMC can be met.
If a yield model is available during the specialist meeting, an additional half a day could be used while the
specialists are all still available to address these aspects. As this action would not necessarily be the norm, this
step is not quantified in the costing of the procedure.
Task XIX(a). Draft notice of RDM determination
A notice must be prepared, in which the class, Reserve and resource quality objectives are listed for each
resource unit. In the intermediate RDM determination, the notice may be a Department policy paper or
statement, rather than a notice in the Government Gazette.
An example notice will be included in the Pienaars River pilot test report, and in the Integrated Manual in
version 1.1 of these manuals.
Task XIX(b). Supporting technical reports
Documentation is required specifying in detail how the RDM were determined and specifically to document the
motivations from each specialist for specified flow, water quality and habitat requirements. All assumptions
must be documented and fully justified.
The report should contain the decision-making process followed during the determination of the RDM and all
motivations. This report need not describe the method which should be available in different documentation.
An example report will be included in the Pienaars River pilot test report, and in the Study Manager’s Manual.
Expertise required: An aquatic scientist who has been involved in the RDM study, with report writing skills,
preferable the team leader /technical co-ordinator.
Time required: Four days
Task XIX(c). Design of post-RDM monitoring programme
The specialist team should design an appropriate post-RDM monitoring programme. The objectives of
monitoring are:
 To collect data to improve the confidence of a future RDM determination at the next level (e.g. to prepare
for a future comprehensive determination if the present determination was at intermediate level);
 To monitor the response of the aquatic ecosystem to the Reserve and RQO that were set, to check that the
Reserve and RQO do actually provide the level of protection required by the selected management class;
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
To monitor resource quality status in order to ascertain whether management actions are adequate to
achieve compliance with the requirements of the Reserve and RQO.
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ADDENDUM E1
Method to convert dissolved oxygen concentration to a percentage saturation
Convert the dissolved oxygen concentration to a percentage saturation by dividing the observed dissolved
oxygen concentration by the theoretical dissolved oxygen saturation concentration.
Dissolved oxygen (%) = (DOobs / DOsat ) * 100
where
DOobs = observed dissolved oxygen concentration (mg/l)
DOsat = dissolved oxygen saturation concentration (mg/l)
The dissolved oxygen saturation concentration is dependent on water temperature and elevation above sea level.
The saturation concentration can be read from a table (Method 1) or calculated (Method 2).
Method 1
Table E1.1: Dissolved saturation concentration as a function of water temperature and elevation
Water
temperature
(degree C)
Elevation
correction
0 to 100 m
Elevation
correction
100 to 400m
Elevation
correction
400 to 800m
Elevation
correction
800 to 1200m
Elevation
correction
1200 to 1600m
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
12.7
12.4
12.2
11.9
11.6
11.4
11.1
10.9
10.7
10.4
10.2
10.0
9.8
9.5
9.3
9.1
8.9
8.7
8.6
8.4
8.2
8.0
7.8
7.7
7.5
12.1
11.8
11.6
11.3
11.1
10.8
10.6
10.4
10.1
9.9
9.7
9.5
9.3
9.1
8.9
8.7
8.5
8.3
8.1
8.0
7.8
7.6
7.5
7.3
7.1
11.4
11.2
11.0
10.7
10.5
10.3
10.0
9.8
9.6
9.4
9.2
9.0
8.8
8.6
8.4
8.2
8.1
7.9
7.7
7.5
7.4
7.2
7.1
6.9
6.8
11.0
10.7
10.5
10.3
10.0
9.8
9.6
9.4
9.2
9.0
8.8
8.6
8.4
8.2
8.1
7.9
7.7
7.5
7.4
7.2
7.1
6.9
6.8
6.6
6.5
10.4
10.2
10.0
9.8
9.5
9.3
9.1
8.9
8.7
8.5
8.4
8.2
8.0
7.8
7.7
7.5
7.3
7.2
7.0
6.9
6.7
6.6
6.4
6.3
6.1
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Method 2
The dissolved oxygen saturation concentration at sea level as a function of temperature (zero salinity) can be
calculated as (APHA, 1985):
ln csf = -139.34411 + (1.575701 x 105 / T) - (6.642308 x 107 / T2) + (1.2438 x1010 / T3) - (8.621949 x 1011 / T4)
where
csf = freshwater dissolved oxygen concentration in mg/l at sea level
ln = natural logarithm
T = temperature in K, T(K) = T(C) + 273.15
The change in saturation with elevation can be approximated as (Zison et al., 1978):
osp = os1 [1 - 0.1148 x elevation (km)]
where
osp = saturation concentration of oxygen at elevation
os1 = saturation concentration of oxygen at sea level
References
APHA (American Public Health Association). 1992. Standard methods for the examination of water and waste
water. 18ed., Washington, DC.
Zison, S.W., Mills, W.B., Diemer, D. and Chen, C.W. 1978. Rates, constants, and kinetic formulations in
surface water quality modelling. US EPA, EPA/600/3-78-105
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ADDENDUM E2
Method to obtain the un-ionised ammonia concentration.
Un-ionised ammonia is dependent on the pH and the water temperature and can be derived from a table showing
the relationship (Method 1 below) or calculated if the water temperature, pH and electrical conductivity (or
TDS) is known.
Method 1
Table E2.1: Relationship between water temperature, pH and un-ionised ammonia
PH
water temperature (degree C)
10
15
20
25
30
6.5
0.06
0.09
0.12
0.18
0.25
7
0.18
0.27
0.39
0.56
0.79
7.5
0.58
0.85
1.2
1.7
2.4
8
1.8
2.6
3.8
5.3
7.3
8.5
5.5
7.9
11
15
20
Method 2
Un-ionised ammonia can be calculated in river water samples from the ammonium concentration using water
temperature, electrical conductivity and pH.
Un-ionised ammonia (NH3) (mg/l) = NH4 / (1 + 10logK-pH)
where NH4 is the total analysed ammonia concentration in mg/l, pH is the pH of the sample and logK is
calculated as follows:
logK = 0.00035130T2 + -0.044736T + 10.119
+ [-0.00055400T2 + 0.029236T + -0.59920]*[sqrt(I)/(1+sqrt(I))]
+ [-0.00021131T2 + -0.0010510T + 0.46909]*I
where T is the water temperature in degrees Celsius (C) and I is the ionic strength in mol/l which can be
calculated from the electrical conductivity as:
I = 0.00013(EC)
where EC is the electrical conductivity in mS/m. This ionic strength: EC relationship is valid for river waters
and soil extracts with an electrical conductivity less than 3200 mS/m.
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ADDENDUM E3
INTERMEDIATE RESERVE DETERMINATION: TOXIC SUBSTANCES4
Sebastian Jooste, Institute for Water Quality Studies, Department of Water Affairs and Forestry
Introduction
The term “toxic substance” must be recognized as a functional term since “toxicity” is defined as the “potential
to cause adverse effect”. It has long been recognized that, in the dictum of Paracelsus, “All things are poison”
(Hathway, 1984). For the purpose of the rapid determination of the reserve those substances listed in the South
African Water Quality Guidelines Volume 7 (DWAF, 1996) will be considered toxic substances.
Whether a substance displays a typical toxic effect depends on the physical and chemical characteristics of the
substance, the state and pharmacokinetics of the exposed population and the physical and chemical processes in
the immediate environment of the individual. The solubility, chemical speciation, chemical stability and
partitioning behaviour could determine the pharmacodynamics driving an effect. The absorbed dose, the
conditions under which a living organism is exposed to the substance, the age, health, diet and general stress,
among others, determine the extent to which an individual organism experiences adverse effect from exposure
to a substance. Environmental factors that will determine the effective exposure of substance, include: the
presence of other toxic substances, the chemical and physical qualities of the environment and the exposure
duration.
For the rapid determination of the reserve it is impossible to bring all these factors into consideration explicitly.
Some assumptions have to be made and for the purpose of the rapid reserve determination these assumptions
will be based on a reasonable worst case scenario:

All substances are considered available and no specific inclusion of chemical speciation is made

The pharmacokinetics and -dynamics are completely determined by the toxicity tests from which the
criteria in the South African Water Quality Guidelines (SAWQG) Volume 7 were derived (DWAF, 1996).

An explicit premise for the determination of the reserve in terms of toxics is that the risk of unsustainability
in an ecosystem is proportional to the risk of irreversibly altering the biodiversity at species level. It is
further assumed that this risk is sufficiently described by the statistical assumptions used in the derivation of
the criteria in the SAWQG vol. 7 (Roux et al., 1996). For administrative simplicity risk categories have
been defined (Table 1)
Table E3.1: Explanation of the risk categories used in the characterization of toxic substance risk
Management
Class
A

4
Degree of risk
Nominal numeric value
Negligible
B
Low
- 10-3
C
Moderate
- 10-1
D
High
Qualitative description
Probability similar to natural global events
which shape changes in the ecosystem (e.g. ice
ages)
Probability similar natural local events which
changes ecosystem (e.g. severe floods,
droughts)
A probability of change that is clearly higher
than that of natural events but which is
acceptable in view of biotic uncertainties
A definite probability of change
It is assumed that the effect experienced by a population (as opposed to an individual organism) is
proportional to both the dose and the frequency of exposure (Mancini, 1983). The dose is addressed
through ambient concentration and the duration of exposure as surrogate parameters. If, as a worst case, it
is assumed that exposure event duration is similar toxicity test duration, so that toxicity test results can be
Editor’s note: to be updated for version 1.1 – check terminology.
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extrapolated without recourse detailed experimental information, then the probability of impact will be
proportional to the frequency of exposure events.
The total toxic risk can be viewed as being composed of two components:
 An ecosystem effect component (E) which is derived from the estimation of the probability of effect based
on the distribution of a benchmark (such as the species mean acute value which is based on the species’
LC50 data) over all the species for which the data exists, and
 An exposure component expressed in terms of frequency () which is either calculated or specified. The
frequency is assumed to represent the probability of exposure. Ideally sampling frequency should be
weekly or daily to correspond with the derivation data. If only monthly data are available, the principle of
maximum entropy requires that the concentration should be considered uniform for 4 weeks at the monthly
value.
The total toxic risk is therefore expressed as the conditional probability P(E/) = P(E)*P(). The values for P(E)
are taken from Table 2 It is assumed that these values, implicit in the derivation of SAWQG criteria, reflect
acceptable risk levels. These levels are used in deriving criteria for the desired state.
Table E3.2: Risk connotation of SAWQG (DWAF, 1996) criteria (from Jooste, 1996).
Criterion
Event description
Risk range (median)
TWQR
Any sub-lethal effect over 3 weeks of exposure
3*10-3 - 5*10-5(3*10-4)
CEV
Any sub-lethal effect in 5% species over 3 weeks exposure
6*10-1 - 6*10--4(2*10-2)
AEV
50% Cumulative mortality in 5% species over 2 days exposure
5*10-2 - 3*10-3(1*10-2)
Mixing Zones
Any effluent that discharges into the stream will take some time to mix into the receiving water. Unless the
discharge stream composition is the same as the receiving water composition, there will be a concentration
gradient in the stream around the discharge point. This area will be referred to as a mixing zone. The mixing
zone is characterized for toxicity estimation purposes as an area where there is a gradual transition from a
transverse discharge concentration gradient to an essentially homogeneous stream. In this area the toxicity
characteristics changes from that of pure discharge to that of proportionally well mixed discharge and receiving
water. These changes can be brought about by either or both dilution (or blending) or environmental
interactions. The Reserve quality specification for toxics is meant to refer to the essentially homogeneous
stretches of the receiving water at the edge of the mixing zone.
In order for a stream to have the capacity for regeneration after a toxic event, it has been assumed that
recolonization can be effected. In order for this to be true, there should be refugia whence the lost species can
migrate. With no other information at hand, it should be assumed that the only source of stream organisms is
colonies of similar organisms in the same stream. It must therefore be stipulated that mixing zones should not
overlap since the effects that can be expected in the mixing zone exceeds that required at the edge of the mixing
zone.
Assessment of current status
In order to assess the current status the analytical data or at least 4 weekly surface water data during the
expected maximum contamination period should be available.
The procedure can be summarized as follows:
For each toxic substance repeat steps 1- 4
 Collect background data
 Make site specific adjustments of criteria
 Collect toxic substance concentration data for the significant water resource
 Assess the current status of the river
The total toxic risk is the maximum toxic risk of any toxic substance in the water
Detailed description of the assessment steps:

Collect background (pristine) concentration data for toxic substances at the significant resource
Clearly anthropogenic substances should be excluded (e.g. pesticides)
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If pristine data is not available, expert advice may be necessary to:
Determine the mineralogy of the upstream catchment
Estimate the equilibrium concentration of metals using MINTEQA2 software (EPA, 1996) based on
this mineralogy
 Adjust criteria:
If 99th percentile(background) > TWQR then
TWQR’= 99th percentile (background)
If median(background) >CEV then
CEV’ = TWQR’*CEV/TWQR
****[ If min(analytical detection limit)< TWQR then
TWQR’= min (ADL)
If CEV < TWQR’ then
CEV’ = 2*TWQR’]****


Collect the toxic substance concentration data for the significant resource
Transform analytical data of lower frequency than weekly to weekly by assigning the last determined value
to the missing weekly slots between analytical data, or by Bayesian analysis of the available data.
Classify the substance analytical data into classes as in Table 3

Table E3.3: Grouping of analytical data for risk estimation
Interval
Nominal acute risk P(Eai)
1



Nominal risk P(Eci)
-5
2
10
3
10-2
4
-1
10
Criterion
5*10
-5
concentration < TWQR
3*10
-4
TWQR  concentration <
CEV
2*10-2
5
CEV  concentration < AEV
concentration  AEV
c) Determine the number of data in each group (n1, n2, n3 and n4) and the relative frequency (e.g. for group
1: 1 = n1/(n1+n2+n3+n4)
d) Assign: P(i) = I and P(Ei) as in Table 3
e) Calculate the acute and chronic risk (Ra and Rc respectively) as:
4
x
R   P( )  P( E xi )
i
i 1
..........[1]
where x is a (acute) or c (chronic). This risk assignment should be adjusted by reviewing the concentration time
series. If there is reason to believe that concentration of a toxic substance is in group 4 for n consecutive weeks
(where n >1), then the adjusted acute risk, Ra’= n*Ra . If there is more than one period where the concentration
is in group 4 then n is the highest number of consecutive weeks in group 4 in the time series. For example, if the
time series indicates that group 4 concentrations appear for 2 weeks and after a break of 2 weeks appear for 3
consecutive weeks, then the adjusted risk Ra’= 3*Ra. The chronic risk is adjusted by a factor nn . Therefore Rc’ =
33*Rc = 27*Rc.


Assess current class
Assign the degree of risk according to Table 1 using the max(Ra, Rc).
Worked example
Given analytical data as shown in Figure 1. There was no reason to expect that either zinc or cadmium appears
naturally in the water at this point. -BHC (GBHC) is a synthetic pesticide and is therefore not considered in the
background estimation.
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6
450
400
5
350
ug/l
4
300
250
3
200
2
150
Cd
GBHC
Zn
100
1
50
25
23
21
19
17
15
13
11
9
7
5
3
0
1
0
Week
Figure E3.1. The weekly analytical concentrations of Zn (secondary Y-axis), total Cd and GBHC
(primary Y-axis).
The data given is already available on a weekly basis, therefore no adjustment need to be made. If for example
the Zn datum at week 10 had been missing, two options could have followed:
 The most unbiased estimate would be assign a value of 416 µg/l to week 10, or
 Given that the Zn concentration of 416 µg/l in week 9 is clearly higher than in either week 8 or 11, it seems
reasonable to assign it a lower value based on the rest of Zn analytical data. A more Bayesian approach
would be to calculate the median, variance and standard deviation of the data and assign week 10 a value of
(median +2*standard deviation) for which there would be approximately 95% confidence that the true value
should be less than that.
The criteria values for the substances are given in Table A
Table E3.4: A Criteria concentrations from the SAWQG Vol 7.
Criterion
Zn (µg/l)
Cd (µg/l)
GBHC (µg/l)
TWQR
37
2.8
1.6
CEV
3.6
0.19
0.1
AEV
2
0.1
0.01
Grouping the analytical data according to Table 3 and calculating the frequentist probability yields results as
shown in Figures 2, 3 and 4
0.56
0.6
0.5
P(v)
0.4
0.32
0.3
0.2
0.08
0.1
0.04
0
x<TWQR
T<=x<C
C<=x<A
x>A
Figure E3.2: Grouping analytical data for zinc
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Resource Directed Measures for Protection of Water Resources: River Ecosystems
0 .9 2
1
0 .8
0 .6
0 .4
0 .2
0 .0 4
0 .0 4
T<=x <C
C<=x <A
0
0
x <TW Q R
x >A
Figure E3.3: Grouping analytical data for cadmium
0.76
0.8
0.7
0.6
P(v)
0.5
0.4
0.3
0.2
0.2
0.1
0.04
0
0
x<TWQR
T<=x<C
C<=x<A
x>A
Figure E3.4: Grouping analytical data for -BHC
The acute and chronic toxic risk is calculated as shown in Table B
Table B Acute and chronic risk. The nominal values calculated from equation [1] and adjusted for duration of
exceedence.
Substance
Nominal Risk
Adjusted Risk
Zn acute
9.6*10-3
9.6*10-3
Zn chronic
2.1*10-1
2.1*10-1
Cd acute
4.0*10-4
4.0*10-4
Cd chronic
8.6*10-3
8.6*10-3
-BHC acute
4.0*10-4
1.2*10-3
-BHC chronic
9.0*10-4
2.4*10-2
Inspection of the time series shows that the AEV for GBHC is exceeded for 3 weeks (weeks 16 to 18) and
therefore both acute and chronic risk has to be adjusted (n=3) by factors 3 and 27 respectively (see column 3 in
Table B).
Based on the maximum risk in Table B, rounded to the nearest unit, (10 -1) and the classification in Table 1, this
water resource may be described as being subject to moderate risk and therefore classed as C.
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Reserve determination
In order to set the reserve, the frequency of exceedence for each citerion in SAWQG vol 7 is set. This is
summarized in Table 4.
Table E3.4: Compliance a table for the determination of the ecological reserve for different management
classes.
Risk target
%TWQR
%CEV*
%AEV**
A
< 10-4
90
99
100
B
< 10-3
-
95
99
C
-2
-
75
90
Management class
< 10
D
< 10
50
85
At no stage should he CEV be exceeded for more than 4 consecutive weeks. If the CEV has been exceeded
for up to 4 consecutive weeks there should be a period of at least 12 weeks where concentrations  TWQR is
maintained.
**
The AEV should not be exceeded for more than 1 week consecutively. If the AEV has been exceeded for up
to one week, it should be succeeded by a period where the concentration is no higher than the CEV of 4 weeks
for Class B, 3 weeks for Class C and 2 weeks for Class D.
*
Notes
 At no time should there be overlap of mixing zone of toxic discharges
 This reserve determination assumes that all stressors act independently. Any interdependence or additivity
among different stressors may change the risk significantly. If there is any reason to suspect that more than
one stressor is present in the receiving water, recourse should be taken to bioassessment to estimate the risk.
References
DWAF (1996) South African Water Quality Guidelines. Volume 7: Aquatic Ecosystems. First Edition.
Department of Water Affairs and Forestry, Pretoria
Hathway, D.E., (1984). Molecular Aspects of Toxicology. The Royal Society of Chemistry, London.
Jooste, S.H.J., (1996). Risk based interpretation of some South African criteria for the protection of the aquatic
ecosystem. Proc. Vic Falls Conf. on aquatic Systems and International Symposium on Exploring the Great
Lakes of the World Food Web Dynamics, Health & Integrity. 15-19 July, 1996, Victoria Falls, Zimbabwe.
Mancini, J.L., (1983). A method for calculating effects, on aquatic organisms, of time varying concentrations.
Wat. Res., 17, pp1355-1362.
Roux, D.J., S.H.J. Jooste and H.M. MacKay, (1996). Substance-specific water quality criteria for the protection
of South African freshwater ecosystems: methods for derivation and initial results for some inorganic toxic
substances. S. Afr. Journal of Science, 92, pp198-206.
USEPA (1996) Exposure Models Library and Integrated Model Evaluation System. EPA/600/C-92/002. Office
of Research and Development, United States Environmental Protection Agency.
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